Automatic External Defibrillators (AEDs) are used by non-medical personnel to defibrillate victims of cardiac arrest the prevalence of which is approximately 600,000 people per year, worldwide. In the past, these AEDs had only been available for the adult population, and the pediatric arrest victims were forced to wait valuable minutes for the professional rescuers such as paramedics, doctors or nurses to arrive. AEDs are now available that are designed specifically to be compatible for use on children. Because defibrillation energies are lower with children, various methods have been developed to accommodate this fact and provide a means of switching defibrillation energies if a pediatric arrest victim is present. One method, described in U.S. Pat. No. 6,101,413, determines a pediatric arrest victim is present if the AED detects that electrodes specifically designed for use with children are attached to the device, in which case the energy levels and voice prompts associated with energy delivery are adjusted to conform with those most appropriate for children. U.S. patent application No. 2003/0195567A1 describes a method that determines a victim is a child based on user input form the AED operator. The energy levels are set based on such indirect means as a measurement of the patient, e.g., the length of an anatomical feature of the victim may be correlated within the AED to a specific energy level.
Resuscitation treatments for patients suffering from cardiac arrest generally include clearing and opening the patient's airway, providing rescue breathing for the patient, and applying chest compressions to provide blood flow to the victim's heart, brain and other vital organs. If the patient has a shockable heart rhythm, resuscitation also may include defibrillation therapy. The term basic life support (BLS) involves all the following elements: initial assessment; airway maintenance; expired air ventilation (rescue breathing); and chest compression. When all three [airway breathing, and circulation, including chest compressions] are combined, the term cardiopulmonary resuscitation (CPR) is used. In the case of pediatric arrest, CPR takes on a heightened prominence based on the fact that cardiac arrest is rare in children, and many more children are affected by respiratory arrest due to choking, drowning, poisoning and asthma.
There are many different kinds of abnormal heart rhythms, some of which can be treated by defibrillation therapy (“shockable rhythms”) and some which cannot (non-shockable rhythms”). For example, most ECG rhythms that produce significant cardiac output are considered non-shockable (examples include normal sinus rhythms, certain bradycardias, and sinus tachycardias). There are also several abnormal ECG rhythms that do not result in significant cardiac output but are still considered non-shockable, since defibrillation treatment is usually ineffective under these conditions. Examples of these non-shockable rhythms include asystole, electromechanical disassociation and other pulseless electrical activity. Although a patient cannot remain alive with these non-viable, non-shockable rhythms, applying shocks will not help convert the rhythm. The primary examples of shockable rhythms, for which the caregiver should perform defibrillation, include ventricular fibrillation, ventricular tachycardia, and ventricular flutter.
The current protocols recommended by the American Heart Association (AHA) are as follows: after using a defibrillator to apply one or more shocks to a patient who has a shockable ECG rhythm, the patient may nevertheless remain unconscious, in a shockable or non-shockable, perfusing or non-perfusing rhythm. If a non-perfusing rhythm is present, the caregiver may then resort to performing CPR for a period of time in order to provide continuing blood flow and oxygen to the patient's heart, brain and other vital organs. If a shockable rhythm continues to exist or develops during the delivery of CPR, further defibrillation attempts may be undertaken following this period of cardiopulmonary resuscitation. As long as the patient remains unconscious and without effective circulation, the caregiver can alternate between use of the defibrillator (for analyzing the electrical rhythm and possibly applying a shock) and performing cardio-pulmonary resuscitation (CPR). CPR generally involves a repeating pattern of five or fifteen chest compressions followed by a pause during which two rescue breaths are given.
Defibrillation can be performed using an AED. The American Heart Association, European Resuscitation Council, and other similar agencies provide protocols for the treatment of victims of cardiac arrest that include the use of AEDs. These protocols define a sequence of steps to be followed in accessing the victim's condition and determining the appropriate treatments to be delivered during resuscitation. Caregivers who may be required to use an AED are trained to follow these protocols.
Most automatic external defibrillators are actually semi-automatic external defibrillators (SAEDs), which require the caregiver to press a start or analyze button, after which the defibrillator analyzes the patient's ECG rhythm and advises the caregiver to provide a shock to the patient if the electrical rhythm is shockable. The caregiver is then responsible for pressing a control button to deliver the shock. Following shock delivery, the SAED may reanalyze the patient's ECG rhythm, automatically or manually, and advise additional shocks or instruct the caregiver to check the patient for signs of circulation (indicating that the defibrillation treatment was successful or that the rhythm is non-shockable) and to begin CPR if circulation has not been restored by the defibrillation attempts. Fully automatic external defibrillators, on the other hand, do not wait for user intervention before applying defibrillation shocks. As used below, automatic external defibrillators (AEDs) include semi-automatic external defibrillators (SAEDs).
Automated External Defibrillators include signal processing software that analyzes ECG signals acquired from the victim to determine when a cardiac arrhythmia such as Ventricular Fibrillation (VF) or shockable ventricular tachycardia (VT) exists. Usually, these algorithms are designed to perform ECG analyses at specific times during the rescue event. The first ECG analysis is usually initiated within a few seconds following attachment of the defibrillation electrodes to the patient. Subsequent ECG analyses may or may not be initiated based upon the results of the first analysis. Typically if the first analysis detects a shockable rhythm, the rescuer is advised to deliver a defibrillation shock. Following the shock delivery a second analysis is automatically initiated to determine whether the defibrillation treatment was successful or not (i.e. the shockable ECG rhythm has been converted to a normal or other non-shockable rhythm). If this second analysis detects the continuing presence of a shockable arrhythmia, the AED advises the user to deliver a second defibrillation treatment. A third ECG analysis may then be initiated to determine whether the second shock was or was not effective. If a shockable rhythm persists, the rescuer is then advised to deliver a third defibrillation treatment.
The typical algorithms process the ECG for measured features which will differentiate the rhythm as shockable (ventricular fibrillation (VF) and ventricular tachycardia (VT)) or non-shockable rhythms (normal sinus rhythms (NSR), abnormal rhythms (ABN), non-shockable VT's and asystole). Some of these features include R to R interval averaging, R to R interval variance, average and maximum signal amplitude, measures of baseline isoelectric time, QRS width, ECG first difference distributions, and parameters from frequency domain analysis1 Analyses of annotated ECG databases establish the distribution of values for a given feature for shockable and non-shockable rhythms. Appropriate decision logic techniques can be used to combine this knowledge and produce the shock or non-shock decision.
Although AEDs have been designed for use on adults and the ECG arrhythmia logic has been developed for the adult population, there is a clear need to extend the use of AEDs to children with cardiac arrest. Recent literature have reported the accuracies of adult based AED arrhythmia algorithms on ECG databases collected from children and have concluded they are safe and effective. However, there are significant differences between adult and pediatric ECG rhythms. For example, the pediatric ECG exhibits faster normal heart rates, narrower QRS widths, and shorter PR and QT intervals as compared to adults. Shockable ventricular tachycardia occurs at much higher rates (>200 BPM) in pediatric subjects than adults (>150 BPM).
Following the third defibrillator shock or when any of the analyses described above detects a non-shockable rhythm, treatment protocols recommended by the American Heart Association and European Resuscitation Council require the rescuer to check the patient's pulse or to evaluate the patient for signs of circulation. If no pulse or signs of circulation are present, the rescuer is trained to perform CPR on the victim for a period of one or more minutes. Following this period of cardiopulmonary resuscitation (that includes rescue breathing and chest compressions) the AED reinitiates a series of up to three additional ECG analyses interspersed with appropriate defibrillation treatments as described above. The sequence of 3 ECG analyses/defibrillation shocks followed by 1-3 minutes of CPR, continues in a repetitive fashion for as long as the AED's power is turned on and the patient is connected to the AED device. Typically, the AED provides audio prompts to inform the rescuer when analyses are about to begin, what the analysis results were and when to start and stop the delivery of CPR.
The AED can be used on adult and pediatric patients. However, the American Heart Association recommends a different protocol in the rescue of pediatric victims compared to the adult rescue protocol particularly with regards to the application of CPR. Because of the heightened prominence of airway and breathing with pediatric arrest victims, the AHA recommends that prior even to calling and activating emergency medical services (EMS) system, the child's airway is first checked for obstructions, the airway is cleared, and mouth to mouth breathing is performed in order to provide what is usually the primary treatment of respiration to the child. The AHA recommends a ratio 15 chest compressions to two ventilations in the case of an adult victim and a ratio of five chest compressions to one ventilation in the case of pediatric victims. The recommended rate of compressions in both adult and pediatric victims is 100 compressions per minute. The rationale for this difference in compression to ventilation ratios is that: 1) the most common cause in pediatric (<8 years of age) arrest is respiratory; and 2) respiratory rates in pediatric (<8 years of age) population are faster than respiratory rates in adults. In addition, the recommended depth of chest compression for pediatric victims (<8 years of age) is 1 to 1.5 inches while the recommended chest compression depth for adult and pediatric (>8 years of age) is 1.5 to 2 inches.
Existing AEDs are unable to provide appropriate rescue protocol and ECG analysis for a pediatric (<8 years of age) victim that is different from an adult rescue protocol and ECG analysis. Also, a lay rescuer who is trained on pediatric resuscitation and is not aware of the AHA guidelines recommendations will not be able to provide an effective resuscitation for a pediatric victim when using these existing AEDs.